Photos

Photos

I am not an artist, my subject is not the dramatics of
lighting, or the esthetics of well positioned props, I am not
interested in the type of photography where the photographer
directs the moment (like in fashion photography).

I like the type of photography where the photographer hunts
the moment (like in photojournalism and event photography). For
me the subject is the human, animal or object which has
determined me to take the photograph.

Essential knowledge

Here is a summary of the most important factors that you must
understand and control.

Sensor size

The most important technical which differentiates the various
types of photo cameras is the amount of light which is captured
for a photo. This amount of light is influenced by the size of
the sensor. The size of the sensor influences in turn the size of
the lens (mainly the diameter, but also indirectly the length).

The bigger a sensor is, the more light it captures for a photo
and therefore the less noise that photo has (and looks
technically better). The "noise" is something like
television static: pixels with random colors and brightnesses.

A compact / pocket camera has a sensor size of about 8 * 5 mm,
most cameras with interchangeable lenses (called DSLR cameras)
have a sensor size of about 23 * 18 mm, while the so called "full
frame" cameras have a sensor size of about 36 * 24 mm. There
are cameras with even bigger sensors, but those are tens of times
more expensive than common DSLR cameras.

The main advantages of a photocamera with a large sensor (=
DSLR) compared to a photocamera with a small sensor (= compact
camera) are:

Higher maximum background
blur; DSLRs can achieve a much higher background blur than
compact cameras can. This means that the foreground and
background planes of the photographed scene have a clearer
separation, which looks better for any type of photography
(other than landscape). (This is an artistic advantage.)

Bigger and brighter viewfinder, which helps you see the
photographed scene better. (This is a technical advantage.)

Focal length

The focal length (measured in millimeters) is the distance
from the lens to the plane at which the photo is formed.

The length of a lens is an indication of a parameter called
focal length; this can be set by rotating a ring on the lens (not
the manual focus ring).

In compact cameras, the focal length is called zoom (and you
usually can't see exactly which value is set). Typical compact
cameras have an equivalent "full frame" focal length of
about 30 mm for zoom 1x (= no zoom), and about 120 mm for zoom 4x
(these relations are proportional).

When you take a portrait, you should stay 2...4 meters (7...14
feet) away from your subject and then change the zoom / focal
length to fill the frame with your subject's head and shoulders.

You can see distortions due to the focal length here
and here.
You can see there that a long focal length (/ high zoom) is
preferable for portraits.

Effects:

Increasing it has a zoom-in effect, that is, it exposes
the camera sensor to a smaller part of the subject.

Increasing it amplifies the background blur, especially
in the far away background.

Distorts depth perception. Short focal lengths amplify
depth (creating a spheric projection of the reality), while long
focal lengths dampen depth (creating a planar projection of the
reality). It's considered that an equivalent "full frame"
focal length of 50 mm creates no distortions relative to what
the human eye sees.

F-number

The F-number is the focal length of the lens divided by the
diameter of the central circular opening of the diaphragm.

The lens diameter is an indication of a parameter called
F-number; this can be set from the camera. The F-number
determines the amount of light which enters through the lens (a
larger diameter means that more light enters through the lens),
and also the depth of the clarity zone (that is, how close or far
is the background blur from the point of focus).

Effects:

Increasing it allows more light to go through the lens
and reach the sensor. The amount of light which reaches the
camera's sensor is inversely proportional with square of the
F-number.

Increasing it reduces the depth of field.

Increasing it reduces the background blur.

Shutter speed

The shutter speed (measured in exposures / second) is the
inverse of the exposure time. The exposure time is the time
during which the camera sensor captures light to form a photo.

Effects:

Increasing it reduces the amount of light which goes
through the lens and reaches the sensor.

Increasing it reduces the effect of (subject or camera)
motion on the clarity of the photo.

ISO

The ISO is a post-exposure scaling factor which is
applied to the light that reaches the camera sensor.

Effects:

Increasing it amplifies the signal (and the noise)
present in a photo, thusly producing a properly lit photo, but
one where the noise destroys more and more details.

Background blur

The background blur is the amount of blur of a subject which
is not in the focus plane, but either in front or behind it.

Effects:

Shrinks with the distance to the subject.

Shrinks with the F-number. Grows with the aperture.

Grows with the focal length. The growth is limited by an
asymptote which increases with the focal length.

Grows with the distance to the background.

Depth of field

The depth of field is the distance range in which the subject
of a photo appears in focus (= clear).

The depth of field and the background blur are very important
for closeups and portraits because they can produce a clear
separation between the subject and the background, separation
which has a very artistic effect.

Effects:

Grows with the distance to the subject.

Grows with the F-number. Shrinks with the aperture.

Is virtually not affected by the focal length, for the
same subject magnification (= subject size in photo).

Various

Knowledge

Aperture (measured in millimeters) = The diameter of
the central circular (really more of an octagon) opening of the
diaphragm. The aperture of a lens is equal with the focal length
of the lens divided by the F-number. A fast / wide aperture means
a large aperture. A fast / wide / large aperture means a small
F-number.

Autofocus = The automatic focusing process achieved by
the camera and the lens. The precision of the autofocus is not
constant and this is one of the factors which, at least in
certain conditions, may turn photos into mere snapshots.

The autofocus is performed at a lenses physical aperture (for
the current focal length), not at the F-number that you've set,
which is very important in low light for focus speed and
accuracy. Some autofocus sensors become active only if the
F-number is smaller than a given value (like F2.8 for the center
cross-type sensor).

Bokeh = The quality of the out-of-focus blur.

Circle of confusion (COC) = The amount of blur above
which a person finds that the objects from a photo do not look
sharp anymore.

The COC is in fact highly variable because it depends on the
type of the viewed photo (on screen, printed or developed), on
the size of the photo (which is normally 10...30 centimeters), on
the viewing distance (which is normally 20...60 centimeters), and
on visual acuity of the viewer.

Color temperature (measured in kelvin) = A
characteristic of light which indicates its tint toward red or
blue.

The complex version of the color temperature is the spectral
power distribution.

The color temperature is used to set the white balance.

Crop factor = The ratio of the diagonals of a reference
camera sensor (36 * 24 mm, 43 mm diagonal, called full frame
sensor) and a compared sensor; this number is normally higher
than 1. Basically, a cropped sensor is a sensor which is smaller
than the reference sensor, that is, it "sees" a smaller
part of a subject; the margins of the frame are cut out from the
photo.

The surface of a cropped sensor is inversely proportional with
the square of the crop factor. For example, Canon EOS 40D has a
crop factor of 1.6 and a surface 2.56 times smaller than the
reference sensor.

Diaphragm = A circular mechanical device (in the
camera) which controls the aperture of the lens.

Dynamic range (measured in stops) = The ratio between
the brightest and darkest spots captured by a camera sensor,
where detail is still visible in the resulting RAW image; this
may be expressed on a logarithmic scale. For example, the dynamic
range of a sensor can be 12 stops, which means a 2048 (= 2 ^ 12)
ratio.

Exposure = The capturing of the light which goes
through the lens, by the camera's sensor.

Exposure compensation = Manually set bias of the
automatic exposure determined by the photocamera, used for
exposure modes like "Aperture Priority". If the taken
image is too dark then set the exposure compensation to a
positive value, and if the taken image is too bright then set the
exposure compensation to a negative value.

Exposure time (measured in seconds) = The time during
which the camera sensor captures light.

Exposure value = The combination of the aperture,
exposure time and ISO. These parameters are responsible for the
physical exposure of photos, and can't be change later.

F-number = The focal length of the lens divided by the
diameter of the central circular opening of the diaphragm. A fast
lens means a small F-number.

The amount of light which (goes through the lens and)
illuminates the camera's sensor is inversely proportional with
square of the F-number. You may be tempted to think that the
amount of light should be proportional with the surface of the
opening through which light enters through the lens, but it's not
so.

Focal length (measured in millimeters) = The distance
from the lens to the plane at which the image is formed.
Increasing the focal length of the lens has a zoom-in effect,
that is, it exposes the camera sensor to a smaller part of the
subject.

Focus = The state in which the subject of a photo has
maximum clarity / sharpness.

Gamut = A subset of the entire range of colors
perceivable by the average human eye.

When you hear that some display is able to show millions or
billions of colors, that does not refer generally to the "amount"
(= gamut) of colors which can be shown, but refers to the detail
of the shown colors (which has little relevance because from some
point the eye can't perceive the difference).

ISO = The sensitivity to the light, of the camera's
sensor.

Magnification = The ratio between the size a subject
projected on a camera's sensor and its real size. Macro lenses
typically have a magnification of 1, that is, a subject 10
millimeters tall also has 10 millimeters on the sensor; in such a
case, if the sensor is 25 millimeters tall, the subject takes 40%
of the photo's height.

Magnification of subject = The percentage of a subject
from the total photo height / width.

If a person is photographed with a camera sensor of a given
size and a given focal length, and then with another camera with
a larger sensor and the same focal length, the subject looks
smaller in the second photo because the larger sensor literally
has more sensor space around the smaller sensor.

In order to have the same subject magnification in the two
photos, the second photo has to be taken either from a smaller
distance or with a longer focal length; the proportion is equal
with the crop factor between the two sensors (= the width /
height / diagonal of the larger sensor divided with the width /
height / diagonal of the smaller sensor).

Metamerism = The matching of colors of with different
spectral power distributions.

Colors reflected by objects may look differently depending on
the spectral power distribution of the light which illuminates
them.

For example, if an object is illuminated with sun light, it
shows certain colors. However, if the object is illuminated with
incandescent light, it shows other colors; also, some of the
colors which were distinct in the sun light, now look the same.
These similar colors are called metamers.

Noise = Distortion of pixel / color information
inherent to camera sensors (= the noise doesn't come from the
outside). The main reason why bigger camera sensors yield cleaner
images is that for the same exposure
(and subject magnification) they capture more light, while their
noise remains relatively the same.

Shutter = A mechanical device (in the camera) which
controls the time of the exposure of the camera's sensor to the
light which goes through the lens.

Shutter speed (measured in exposures / second) = The
inverse of the exposure time. A fast shutter speed means a small
exposure time.

Spectral Power Distribution (SPD) = A large set of data
which describes the energy per unit area per unit wavelength of
the light.

The spectral power distribution of the light is of critical
importance in color perception
because physical colors are not simple sets of RGB values (as
their are in photocamera sensors and computer displays). In fact,
a physical color is a complex set of energy data at all the
wavelengths visible to the human eye, which the eye transforms
into a more simple set of data recorded with its rode and cone
cells.

For example, an orange does not emit orange light. Instead, it
absorbs all the wavelengths of the illuminating light except for
a reflected set of wavelengths with different energies which
people perceive as orange.

The simplistic version of the spectral power distribution is
the color temperature.

Stop = A doubling or halving of the amount of light
which goes through the lens.

Stop down = A halving of the amount of light which goes
through the lens. This is equivalent with a doubling of the
shutter speed (because this means that the camera's sensor is
exposed to less light), and with a decrease of the aperture of
1.4 times (it's actually square root of 2).

In general, cameras display their shutter speed and F-numbers
in (approximations of) thirds (or halves) of units in order to
make it easier for the photographer to manually control the
exposure, that is, to know how much the camera would expose an
image.

Stop up = A doubling of the amount of light which goes
through the lens. This is equivalent with a halving of the
shutter speed (because this means that the camera's sensor is
exposed to more light), and with an increase of the aperture of
1.4 times (it's actually square root of 2).

Tonal break = A visible outline (in an image) caused by
an insufficient tonal range along the outline. If the tonal range
were higher, the outline would be a smooth gradation.

Tonal range = The number of tones which show detail
throughout the dynamic range; this may be expressed on a
logarithmic scale. For example, the tonal range of a camera
sensor can be 14 bits, which means 16384 (= 2 ^ 14) intervals.

Unit area = an absolute measurement unit for areas,
like a square millimeter.

White balance = The real color of objects, as seen by
the human eye or photocameras, depends on the color temperature
of the light which reaches them. White balance refers to the
adjustment of colors so that the colors from a photo look similar
to those seen by the eye in normal daylight conditions.

White balance is crucial for indoors photos, photos which have
a color cast from the incandescent or fluorescent light bulbs.

Zoom = The ratio between two focal lengths. An increase
of the focal length of a lens results in a decrease of its angle
of view, which means that a smaller part of the subject is
exposed to the camera sensor, which means that the subject is
zoomed-in (that is, its size is increased on the sensor). A
camera's crop factor doesn't affect the zoom.

Human eye

People see things differently than a photocamera captures
images. The human eye continuously sends images to the brain;
also, different cells from the eye send parts of the viewed
images in different ways: some faster, some slower. The eye
adapts to the environmental light.

People can see very short (single) flashes of light, even
shorter than 1/200 seconds, because the light stimulates the
cells from the eye and it takes some time for them to become
unstimulated, that is, for the stimulus to dissipate. If the eye
cells are stimulated with another (similar) flash before they
become unstimulated, the eye perceives a continuous light.

There is also a difference between a perceived flash light and
what the brain can interpret (in order to recognize a color, a
shape or an object).

Background blur

The background blur is the amount of blur of a subject which
is not in the focus plane.

The background blur:

Shrinks with the distance to the subject.

Shrinks with the F-number. Grows with the aperture.

Grows with the focal length. The growth is limited by an
asymptote which increases with the focal length.

Grows with the distance to the background.

The more blurry the background is, the more the subject "pops"
out from the image.

Depth of field

The depth of field (DOF, or depth of field of clarity) is the
distance range in which the subject of a photo appears in focus.

The depth of field:

Grows with the distance to the subject.

Grows with the F-number. Shrinks with the aperture.

Is virtually not affected by the focal length.

The depth of field beyond the subject is always greater than
the depth of field in front of the subject.

The closer the camera is to the subject (in focus) and the
farther the background is from the subject, the higher the
background blur is and therefore the more the subject "pops"
out from the image.

Use a high aperture (= small F-number) and a long focal length
in order to blur the background and create a beautiful closeup
(like a portrait). Use a low aperture (= high F-number) in order
bring the entire range from the foreground to the background into
focus.

The depth of field and the background blur are very important
for closeups because they can produce a beautifully blurred
background.

Angle of view

The angle of view is the angular extent visible in a
photographed scene. The angle of view decreases as the focal
length of a lens and the crop factor of a camera increase.

A photocamera (like the human eye) sees a scene in a conic
manner, that is, the observed objects are within a cone which
starts as a point at the lens (/ eye) and ends at infinity as a
huge area.

Because a photocamera sees a scene under an angle of view,
objects of a given absolute size appear to have different
relative sizes (on the camera's sensor) when they are located at
different distances from the lens (/ eye). For example, if you
look at a mountain from its base, it will look massive to you
(that is, it will occupy a huge portion of your visual field),
but if you look at it from far away, it will look tiny (that is,
it will occupy a small portion of your visual field).

Sometimes, it's not just an entire object that appears to have
a different size, but also parts of an object. For example, when
photographing a building from a small distance, at ground level,
the top of the building will appear smaller than its base. This
happens because the distance to the top of the building is
significantly larger than the distance to the base of the
building, and as such the top will occupy a smaller area (than
the base occupies) on the camera's sensor. If you would
photograph the same building from far away, the difference
between the distances would be too small to be noticeable.

Perspective distortion

Perspective distortion is a visible alteration of absolute
measures.

Think at photos taken of movie stars (on the "Red
Carpet"). Their feet look thin and their heads look big.

Such photos must be taken from very close to the subject, or
risk having obstacles in between, and therefore in order to frame
the entire subject they must be taken with lenses with a short
focal length.

Now think at the position of the camera. It's usually at the
level of the subject's head.

Because of this, the distance from the camera to the subject's
head is significantly smaller than the distance from the
camera to the subject's feet. Therefore, X centimeters measured
over the subject's head take a specific number of pixels on the
camera sensor, and the same X centimeters measured over the
subject's feet take a significantly smaller number of
pixels on the sensor; this is because objects which are father
away appear smaller (than closer objects).

This is why the feet of the subject appear so thin when
compared to their head.

In opposition to this, when taking a photo of the same subject
with a lens with a long focal length from farther away (in order
to preserve the size of the subject on the sensor), the
differences between the distances become insignificant (, making
the photos look flatter / 2D).

To summarize, taking photos with a lens with a short focal
length exaggerates the differences between the distances to the
various parts of the subject, while taking photos with a lens
with a long focal length flattens / compresses the differences
between the distances to the various parts of the subject
(relative to the distance to the subject, which keeps
increasing).

Taking photos with a lens with a short focal length is not
good for portrait photography, and a long focal length may
require too much of a distance between the photographer and the
subject, which is why the preferred focal length for this is
somewhere between 85 and 135 mm, depending on the crop factor of
the sensor. In portrait photography, a very high
background blur is also desired, which in turn requires
either a wide aperture or a short distance to the subject (and at
the same time a large distance to the background, and possibly
small subjects in the background so that their details can easily
disappear in the blur).

Although taking photos with a lens with a long focal length
flattens the differences between the distances to the various
parts of the subject, thusly showing all the objects from a photo
at their real proportions, this is still called perspective
distortion because it's unnatural for the human eye to see this
flattening of distances.

High ISO look-and-feel by light intensity

Photos taken at a high ISO in sunlight with a good intensity
exhibit a lower noise level and look better than those taken in
low light because:

The dynamic range of scene illuminated with intense
sunlight is higher than the dynamic range of scene illuminated
with low light. This is because the environmental light reflects
on atmospheric particles and on everything it touches, so it
creates a sort of a floor for the light which will be captured
in a photograph. But if the light which falls directly on the
photographed subject is high then the ratio between the
intensity of this light and that of the floor light is high,
hence the dynamic range is high. If the light which falls
directly on the subject is not intense enough compared to the
floor light, the dark tones are downed by the floor light.

The intense sunlight has a spectral power distribution
which better matches that of the sensor's photosites, which
means that the tonal resolution of the photos taken in such
light is much better.

The noise from a bright scene exists mainly due to photon
noise, not due to the electronic / read noise. Photon noise
increases with the brightness but only as the square root of the
number of photons absorbed by the sensor, so the signal-to-noise
ratio of bright scenes is higher than that of dark scenes. Read
noise is relatively stable and does not increase with
brightness.

Light changes with focus

In some lenses, changing the focus range from infinity to the
minimum focusing distance (MFD) decreases the amount of light
that goes through the lens (even though all the other exposure
parameters are the same). This is typical for macro lenses.

To experiment, set the camera and the lens in full manual
mode. Focus-out completely, at infinity, point the lens at a
white wall and take a photo. Now focus-in completely, at the
minimum focusing distance of the lens and take a photo. If you
compare the two photos you can see that the second photo is
(much) darker.

For lenses whose barrel extends when focusing-in, it appears
that the amount of light which goes through the lens decreases
linearly with the length with which the barrel extends.

As an example of this, for the Tamron 90 mm (whose barrel
extends when focusing-in) the second photo has about 2 stops less
light than the first photo. When the barrel is half extended, the
taken photo has about 1 stop less light than the first photo.

For the Canon 70-200 mm the second photo has about 1/3 stops
less light than the first photo, that is, virtually no light
loss.

Filters

A protection filter doesn't visibly decrease the amount of
light that goes through the lens.

Use a polarizing filter to eliminate reflections from
non-metallic objects, like vegetation. The lack of such a filter
can, for example, ruin the photos you take to vegetation after a
rain.

A circular polarizer filter decreases the amount of light that
goes through the lens with 1...4 stops. For example, a Hoya HD
Cir-Pl takes about 1 stop (regardless of its rotation angle).

Rotate the mobile part of the circular polarizer filter to
achieve the effect that you want.

Use this filter with care because it may affect the colors in
an undesired way.

Pixel count

Current photocameras with Bayer sensors, like the usual Canon
and Nikon photocamera, claim to have resolutions of X pixels
(like 10 mega pixels). However, this is in fact the number of
photosites, not pixels.

A photosite is really a monochromatic sensor, normally for
either red, green or blue colors. They are arranged in a matrix
of RGGB patterns (that's two photosites for green).

The reason why photos taken with such camera sensors really
have X pixels is because the software which converts the sensor
data into an image interpolates each photosite to an RGB pixel,
also using the data from the surrounding photosites. This means
that while you expect the software to convert each RGGB pattern
to an RGB pixel, it really doesn't do that; in reality, it
upscales the image 4 times.

This upscaling is a good approximation of an image with the
same number of pixels because it contains certain information (=
luminance resolution) to which the human eye is more sensitive
than it is to color.

Exposure calculation and
camera sensor size

The exposure of a photocamera is calculated per unit area (= a
square millimeter) of the camera sensor because a unit area
receives the same amount of light no matter what the total sensor
area is.

In photocameras, the sensor size and the diameter of a lens
used for it are proportional, so that for each unit area of the
sensor there is a corresponding unit area of the lens, which
means that each unit area of the sensor receives the same amount
of light.

However, this means that larger sensors capture a higher total
amount of light than smaller sensors, and that the images formed
on larger sensors are brighter than the images formed on smaller
sensors. This doesn't mean that the photos taken with larger
sensors are brighter, since such photos are not viewed at a
similarly increased size (they are viewed on the same displays
and printed on the same paper).

There is, however, a consequence of this phenomena: the higher
amount of light captured by the larger sensor overwhelms the
noise, which means that the photos taken with it have lower noise
levels if they are taken with the same subject magnification
/ size (which is usually what photographers do).

Different approach

In current camera sensors, the size of a photosite (in other
words, resolution) has no visible effect on the noise
level of the entire photo (= it only affects the noise
level of the individual photosites). The only thing that matters
is the size of the sensor (well, obviously, besides the
technology).

The reason why there are sensors for phones, for compact
cameras, for DSLRs, for medium format, and... telescopes, is the
size of the sensor, not the size of the photosite. The
bigger the light capturing device (= lens + sensor) is, the more
light is captured for the same exposure.

It's difficult for people to understand that a bigger sensor
means that the photos taken with it contain more light for the
same exposure. They ask themselves where did that light go
because they don't see brighter photos. The answer is simple: the
photos are scaled to the same physical size (but the scale factor
is smaller, because the sensor size is scaled to the same display
/ paper size), so the light goes instead into annihilating the
noise.

ISO and noise level in the shadows

A photo taken with a high ISO exhibits a lower noise level
than a photo taken with a low ISO, in the shadows.

The explanation is that while the camera sensor has a certain
dynamic range, the rest of the camera circuitry (through which
the photons and electrons pass in order to form an image) has a
lower dynamic range, so the noise floor for different ISOs is
different.

Color perception

A color is a combination of several factors:

The spectral power distribution of the light which
illuminates the colored object.

The way in which the spectral power distribution of the
illuminating light is changed when the light is reflected by the
colored object. This change depends on the full spectral power
distribution (not only on the relative spectral power
distribution), that is, it depends on the intensity of the
illuminating light.

Atmospheric reflections (usually caused by dust and
smoke). These may cause a reduction of the contrast (where
blacks turn to gray), or a compression of the black tones (up to
the point where they become mudded / indistinguishable).

The way in which the spectral power distribution of the
reflected light is recorded by a photocamera sensor or by the
eye (and interpreted by the brain). This change depends on the
full spectral power distribution (not only on the relative
spectral power distribution), that is, it depends on the
intensity of the illuminating light.

A color perceived by the human eye is a spectral power
distribution function of an illuminating light which is altered
when reflected by matter into another spectral power distribution
function and then read by the human eye and altered into a much
more limited spectral power distribution function (by the so
called RGB receptors), and finally processed by the brain into
something we perceive as color.

For natural color appearance, the spectral power distribution
of the illuminating light must be as close as possible to that of
the natural sunlight (actually it's a standard called D65).

An object exhibits different colors in different lighting
conditions, even if only the intensity of the illuminating light
is different.

For example, the color sensitivity of the human eye for red is
high when the light is intense, but as the light gets dimmer, the
sensitivity for red decreases in favor of blue, that is, all the
colors are shifted toward blue.

This is why using light bulbs with the same color temperature
as day light (6'500 Kelvin) gives a bluish tint to all objects,
while light bulbs with a lower color temperature (like 4'000
Kelvin) gives a neutral tint; the average incandescent light bulb
has a color temperature of about 2'700 kelvin, which gives a red
tint to all objects.

If the light bulb with a color temperature of 6'500 Kelvin
were to give a light as intense as the day sun, then it would
give no tint to the illuminated objects. However, the light from
the average light bulb is several thousand times less intense
than the light from the day sun.

The dynamic range and tonal range of a photographed scene
depend on the intensity of the illuminating light. If the light
intensity is too low, both ranges are low and the photos took in
such conditions look rather gray. If the light intensity is too
high, the photos are too contrasty, with blown out (= without
detail) shadows (= blacks) and highlights (= whites).

From a technical point of view, photos look their best when
their dynamic range is at a medium value, and their tonal range
is at the maximum value. This is achieved when the intensity of
the illuminating light is at a medium value. Basically, both
ranges have to cover the optimum intervals perceived by the human
eye.

You can see here
how the environment looks like when lit with light of various
color temperatures.

Light intensity

Here is the usual light intensity for a few common cases:

Livingroom: 50...200 lux.

Heavy overcast day: 1'000 lux.

Bright daylight (not the Sun itself): 10'000...100'000
lux.

The perception by the human eye of the light intensity is not
linear with the intensity, but with the type of the light source,
with the environmental light intensity, with a power of the
intensity, and with its color (or more accurately, with its
spectral power distribution).

Due to the complexity of the factors involved, the actual
correlation equation depends on the application. For a general
application, Stevens'
power law is used. You can read more at Telescope
Optics.

Color temperature

The Kruithof
curve correlates color temperature and intensity, from a
visually pleasing point of view.

A light with a low color temperature gives a warm appearance
(red, orange, or yellow), and a light with a high color
temperature gives a cool appearance (blue or white). The sunlight
at the noon of a bright summer day has a temperature of
5'500...6'500 Kelvin. Incandescent light bulbs have a color
temperature of about 2'700 kelvin.

In photography, the color temperature is upside down due to
psychological reasons. A high temperature is used to indicate a
warm color (yellow or red, which have a low temperature in
physics), while a low temperature indicates a cool color (blue,
which has a high temperature in physics).

Spectral power distribution

Each spectral power distribution set distorts the colors of
the illuminated objects compared to other SPDs, whether the light
comes from a natural source such as sunshine, dawn, sunset, or
electric sources such as incandescent and fluorescent light
bulbs.

Effectively, each point of a photographed scene responds
differently, depending on the properties of the light which
illuminates it, in such a way that it makes it impossible to
obtain its standard color from its perceived color by applying
color corrections (like white balance) on the entire photo.
"Standard color" refers to the color which is obtained
by photographing a scene in standard / D65
light. This is why photos taken in bad lighting conditions are
simply bad (from a technical point of view).

The spectral power distribution is the reason why white
balancing photos doesn't always yield the desired results. Each
object from a photographed scene responds differently to the
illuminating light, so white balancing a part of a photo may
destroy the white balance of another part of the photo. This
happens usually when the illuminating light is artificial.

Color correction

Some lighting conditions produce good or acceptable colors,
while others produce bad or horrible colors. In other words, some
lighting conditions produce colors which can be corrected so as
to be similar to those produced in standard D65 light, while
others produce colors which can't be corrected no matter what.

For example, sodium light stimulates matter only on a very
narrow wavelengths band, while sun light stimulates matter on a
very wide wavelengths band.

In such lighting conditions, the colors recorded on the
photocamera sensor can't be corrected with a white balance
because they are either literally not reflected by the matter, or
they are recorded by the sensor as a metamer rather than the
standard color (that is, colors which would be distinct in a
standard D65 light, are the same in sodium light).

You can get acceptable colors in some indoor ligthing
conditions, but some ligthing conditions are just bad.

Color corrections can be done with a custom white balance
(using a gray card), but such cards only record what gray looks
like (which gives an incomplete description of the illuminating
light).

Color corrections can be done more accurately with a Color
Checker, because this records what a large set of colors looks
like in a given light. The associated software then reverse
engineers the standard D65 colors.

Unfortunately, a photocamera sensor doesn't record the
spectral power distribution (= the powers for all the
wavelengths) at each pixel, but only the powers for the RGB
wavelengths. So, in some cases, color corrections can't produce
acceptable colors.

Background blur

Here are some graphs which depict the background blur for
several photo setups.

The X axis represents the distance from the point in focus
(not from the camera) to the background, and is measured in
meters. An X higher than 0 represents the background.

The Y axis represents the blur of the background (beyond the
point in focus), and is measured in micrometers. The blur is 0 in
the focus point (0 on the X axis), that is, the objects from that
point are in perfect focus.

The higher the value on the Y axis, the higher the blur is.

The red line represents the COC for Canon EOS 40D: 19.

If the blur is smaller than the COC (of the camera) then the
blur at that distance would be imperceptible in a photo.

We use the following formula (derived from here)
for calculating the background blur: b = f ^ 2 / (s - f /
1000) / N * |x| / (s + x) , where "b" is the blur
(in micrometers), "f" is the focal length (in
millimeters), "m" is the subject magnification (on the
camera's sensor), "N" is the F-number, "s" is
the focus distance (in meters), "x" is the distance
between the subject and the background (in meters). A negative
"x" yields the foreground blur.

For the far background, the blur has an asymptote which can be
approximated with: f ^ 2 / s / N . This asymptote is
reached when the distance to the background is significantly
larger than the focus distance.

We consider that all lenses take photos of a subject at the
same magnification (= size in photo).

Magnification formula: m = f / (s - f) .

In order to preserve the magnification of lens 2 the same as
the magnification of lens 1, we use the following formula to
calculate at what distance from the subject should lens 2 be: s2
= s1 * f2 / f1 .

The format of the camera's sensor is not a direct factor of
the equation. However, the magnification (and consequently the
focus distance) and the COC depend on the format.

COC formula: coc = sd * va * vd / pd , where "sd"
is the sensor's diagonal, "va" is visual acuity of the
average human eye, "vd" is the viewing distance of the
photo, "pd" is the photo's diagonal.

The average human eye can see (according to this),
in normal light, up to 50 black-white line pairs, contained
within 17.5 millimeters, from 1 meter away. This gives a visual
acuity of 0.35 millimeters from 1 meter away (about 1 / 3000).

The vd / pd ratio is matter of preference. Personally,
I view postcards from a distance equal with 2 to 3 times the
photo's diagonal, an A4 photo from a distance equal with the
photo's diagonal, while a full screen photo on my display from a
distance equal with 1 to 3 times the display's diagonal.

A common COC formula (found here)
is coc = sd / 1500. To obtain this formula, in DOF
calculator you have to use a "Desired COC multiplier"
of 2.

You can see in the graph above that the 85 mm lens has the
highest blur for the most part of the background.

When the focal length and the F-number are multiplied with the
same factor, far away in the background the lenses have the same
asymptote.

For a given F-number and subject magnification, the depth
of field is barely affected by the focal length, the effect
is getting smaller as the focal length increases.

For example, for Canon EOS 40D, with a lens set at F4, a 20 mm
focal length focused at a distance of 2 meters has a 1.72 meters
DOF, a 200 mm focal length focused at 20 meters has a 1.48 meters
DOF, and a 2000 mm focal length focused at 200 meters has a 1.48
meters DOF.

However, because the asymptote of the background blur grows
with the focal length, the far away background plane appears more
clearly separated from the focused plane when a long focal length
is used, and this gives a more pleasing aspect to portraits.

DOF calculator

DofCalc
is web-browser based application which calculates the depth of
field for a given set of photographic parameters.

DofCalc is an open source
application developed in HTML and JavaScript, specifically
designed for mobile devices (like PDAs).

You can download it on your
computer by right-clicking here
and choosing "Save link as". Then just click on that
file to open it in your web-browser and use it.

First public release of
DofCalc:
version 1.0 on 09 June 2009.

Tips

Photography is about perception/
emotion, which is influenced by geometry (=
composition, distortions due to the focal length and angle of
view, depth of field / background blur), which is influenced by
light (= natural or artificial, mood giving), which is
influenced by directing, which is influenced by the scene
(= subject + background).

Post-processing is used to alter the light / color and
geometry after the fact.

Things which make a good photo:
the moment (= the event, the feeling, the emotion, the message,
the uniqueness), action, light, color, people.

A good photo is made by the
subject, lens, camera and editing software, not by the
photographer. The photographer is there to simply capture the
moment and bring forward its soul, not make it.

The most important thing about light is not its amount, but
its properties, like: color (or more accurately: spectral power
distribution), the lack of reflections either in the atmosphere
or from the photographed objects, the limited light contrast
(between shadows and highlights), the high color contrast.

Things which may destroy a good photo

Missed focus: focusing either in front or behind the subject.

Inappropriate depth of field: too shallow for macros or too
deep for close-ups.

Framing only a part of the subject: for example, the subject's
legs are outside the frame.

Use both the landscape and portrait formats

The usual format of a photo is landscape because this is how
the camera sensor is positioned in the camera, as the camera is
held in its most comfortable position. Turn the camera vertically
to take photos in a portrait format. Individual people or flowers
are easier to isolate this way, so they may look better.

Use the flash outdoors

A strong sun light causes a strong light contrast. You can
eliminate the shadows made on people's faces by lightening the
subject with a flash. This is called a fill flash.

Be aware of the light

Avoid taking photos facing sources of strong light, like the
sun.

Avoid taking photos of people facing strong sources of light
because they will squint.

When taking photos of people in strong sunlight, position
yourself to have the sun in front of you, 45 degrees at your
side. Otherwise, the strong light will create strong shadows.

Early or late in the day fills the environment with a golden
light.

Very good conditions for outdoor portrait photography are when
the sun is covered by a thin layer of clouds which diffuse the
light and thus eliminate shadows on the ground. Shadows are the
main cause for ruined outdoor portrait photography, although they
are sometimes used for establishing a mood.

A low ceiling of white clouds may cast a diffuse light which
brings out the (saturated) color of the landscape.

Hold the camera steady

If you can't put the camera on something steady, like a
tripod, hold it with a hand on the side which has the shutter,
and with the other hand support the lens from beneath.

Shutter speed - focal length

In order to take sharp photos while hand-holding the camera,
without image stabilization, use a shutter speed equal with or
higher than the focal length.

For example, if you're using a lens with a 100 mm focal length
then use a shutter speed equal with or higher than 100. If you're
using a lens with a 200 mm focal length then use a shutter speed
equal with or higher than 200.

Get to the subject's eye level

This may mean squatting so that the camera would be at the
subject's eye level, like when you are photographing a child.
This makes the photo more personal.

Get close to the subject

For photos with a more personal touch, fill the entire frame
with the subject.

The background matters

The background (either in front or behind the subject) is at
least as important as the subject.

Don't center the subject

An off center position, in landscape format, for the subject
is usually better than a centered one. This can be done later by
cropping the photo more on one side.

Photographed subjects are not three-dimensional

This is for various reason, but one of them is that a
photograph doesn't show the subject three-dimensionally, as your
eyes do. Therefore, you have to find an angle which gives depth
to the subject.

For example, a flower looks beautiful to your eyes from front,
but when you're taking a photo of a flower you should try an
off-center angle.

Focus the entire subject

If the entire subject's depth appears in focus, the photo
appears clearer / sharper. However, extending the depth of field
too much makes the background look less attractive.

Generally, the closer you get to a subject, the higher the
F-number must be in order to create a greater depth of field.

Long exposure times

When taking photos with a long exposure time (like 1/10
seconds), take them in continuous shooting mode. You'll have a
greater chance to get one of them sharp.

Take photos of people when they are not posing

Taking photos of people who are not preparing to be
photographed gives a natural look to the photos.

Protect the highlights

When you have to deal with a very high dynamic range
(colloquially known as a contrasty situation), like an
illuminated patch of trees whose trunks are in the shadow, make
sure that you record the images in RAW format, and that the image
contains properly exposed bright areas (you will get nearly black
dark areas).

Then, in an editing software lift the shadows as much as you
can. This will brighten the dark areas of the image and will give
the image a look closer to what you have seen with your eyes,
closer to what professional photographers publish, and very
different from what you are used to see from an amateur camera.

If you try to protect the dark areas instead of the bright
ones, therefore exposing the dark areas properly and getting
nearly white bright areas, it's most likely that the processed
image will have very distorted colors, especially in the bright
areas.

In other words, it's far easier to recover the shadows (with
editing software) than the highlights, so it's better to protect
the highlights when the image is taken.

Photos can't be taken in all conditions

While pictures can be taken in any environmental conditions,
to any subjects, photos can not because the conditions either
don't convey anything of importance to the viewer, or the
lighting is really bad.

Never share bad photos

Never share bad pictures, especially of people. Delete
them immediately. Make sure people get good photos of themselves.
After a while you'll gain a good reputation and people will feel
much more at ease with you taking photos of them.

Clear the skin defects, like zits, blemishes and moles. They
distract the viewer's attention to an exaggerated level, and hide
the underlying beauty of the bones, muscles and skin.

Long focal length

Taking photos with a long focal length produces a sensation of
special harmony. This happens because:

Perspective distortion makes objects with equal absolute
measures (in meters), located at different distances in the
frame, occupy a similar number of pixels in a photo. This way,
all the objects from a photo are shown at their real
proportions. Even though this is not natural to the eye, it
looks beautiful.

The viewer is "taken" / "flown" to
the subject, as if zooming live into the frame of the photo,
especially if the foreground is also blurred and the subject
occupies only a part of the frame.

Choosing a lens

When you choose a lens over another, there are several
characteristics that you have to consider:

The focal length range allows you to zoom in or out, and
to alter the perspective distortion of the subjects.

The minimum F-number allows you to maximize the light
gathering capabilities, and the depth of field.

There is no lens which is better than others for taking
portraits, it all depends on what distortion you are trying to
get, and on what space is available from you to the subject.
While a small minimum F-number allows you to get a beautiful
background blur, it also decreases the depth of field so much
that you get a blurry portrait.

Cleaning glass

Wipe the entire surface of the glass (from a lens or a filter)
with a wet microfiber tissue (moistened with ethanol), in a
circular manner, in order to remove dust; a dry tissue may
scratch the glass. The tissue must be label for cleaning glass.

Do this as rare as possible because the ethanol will
eventually strip the delicate coating off the glass. Generally,
dust will not show on photos, so there is no real need to remove
it.

Then, before the moisture evaporates (which does quickly),
wipe the glass with a dry tissue until all the moisture is gone.

If you exhale on the glass, you'll see the moisture from your
breath condense on the glass and expose the cleaning pattern;
this moisture evaporates quickly.

Various

Canon EOS cameras automatically lock the exposure when
"Evaluative" metering and "One-Shot"
auto-focus mode are used. Simply press the shutter button
half-way and both the focus and the exposure will be locked. Good
for shooting portraits: lock on subject, then recompose.

Look at photos on a professional display. A notebook display
is usually limited in its capabilities to reproduce colors. A
good choice is to print the photos.

Sometimes, colors look better if the photo is underexposed. I
find this to be true even for an underexposure of more than 1
stop.

Edit photos

The most important thing that amateur photographers miss is
the extra step that professional photographers are taking: photo
editing (also called post-processing) with the explicit goal of
making the photos consistent (with what the photographer wants).

The problem with the photos taken by the camera is that they
are perceptually inconsistent. The camera records the reality
with a number of hardware parameters which can't be change later.

Everything else done by the camera to output a photo is just
post-processing, that is, the modification of photos after they
were physically recorded, using software.

If you are taking photos using a semiautomatic photo mode,
that is, a mode where the camera automatically computes at least
one of the hardware parameters, the camera will miss (usually by
a small amount) a lot of times to use the hardware parameters
that a photographer would use if he would have the time to
manually set them.

Moreover, reality is not consistent. Light (amount, spectrum
and directionality) and subject colors vary all the time.

Reality is boring, grayish. When taking landscape photos,
you're also facing the problem of atmospheric conditions, usually
in the form of suspended dust particles which reduce the contrast
of distant subjects (making them look grayish).

A significant part of reality is always lost in its path to be
seen as a printed photo (or as one displayed on a computer
screen). The factors which generate a loss of reality are: light,
camera lens, camera sensor, camera hardware parameters, photo
post-processing, printing photos (= paper, ink and quality),
displaying photos on a computer screen, the light in which the
photos are seen, the eyes of the viewers.

Editing photos is the only way to bring the technology of the
camera-display pair on par with the human eye. A camera records a
scene in a colorimetrically correct manner, but the
camera-display pair is literally incapable of reproducing the
same scene that the photographer has seen with his own eyes. A
camera and a display exceed the human eye on some levels, but on
things like dynamic and tonal range the human eye is still
superior and will be so for quite a while.

Also, the eyes of the photographer were physiologically
adapted to the photographed scene, but those of the viewers are
adapted to the environment in which they see the photos.

In the end, the reality seen by the eye of the photographer is
less important than what the viewers of the photos see. The only
good photos are the ones which look good to their viewers.

People see the grayish reality everyday, so why not make it
look better in photos?

Editing photos is like using the manual exposure mode from a
camera. Edit your photos to fit your taste! Don't worry about
details not looking right anymore (because, for example, you've
increased the contrast), a photo looks good when viewed overall.

Lighting

Beauty dish

A beauty dish is a parabolic light reflector (= indirect light
source) where the light beams converge in a focus point, creating
a balance of hard and soft light.

It has an optimal distance from the subject, usually about
twice the dish diameter.

The light created is between that of a direct flash and a
softbox. It is evenly spread and has good feathering at the
edges, and it gives the image a wrapped, contrasting look.

The light is crisp, detailed, delicate, smooth, luminous.

It is great for portraits, beauty and fashion images.

Various

Generally, the closer an umbrella / softbox is to the subject,
the softer the light is, and the farther away it is, the more
directional and harder the light is. Note that the larger the
umbrella / softbox is, the farther it can be moved from the
subject while maintaining the soft light.

Editing flow

It is essential to follow the same editing flow in order to
get consistently good photos.

Make sure you put your name in the camera's settings, so that
all the photos can have a known author.

Take photos in raw format! Taking
photos in raw format and then adjusting them on a computer,
compared to taking photos in JPEG, is as different as day from
night.

From Lightroom, import the
photos from the photocamera to a "Originals" directory,
in a subdirectory named "YYYYMMDD", where "YYYYMMDD"
is the date when the photo was taken. Name the files
"YYYYMMDD_index". Use your own development preset,
created specifically for all imports, which is your starting
point for editing.

Look (several times) through the photos and delete the bad
ones and the redundant ones; maybe edit the photos for the basic
things. Keep maximum 100 photos (between 50 and 200, depending on
the intended audience) from a day's work, or more in exceptional
cases. (Instead of Lightroom, you can use IrfanView
because it loads the preview JPEGs from the RAWs, which is very
fast).

Culling aggressively your photos will help you develop an eye
for artistic detail and you'll become more demanding of your
work. This also minimizes both the space taken by the photos and
the time required to edit them. At the same time, they are not
either too many or too few photos to show to your friends.

Tag the photos with keywords; also rate them. Here are some
examples of keywords: "Animals", "Landscape",
"Making of photoshoot", "Models", "Objects",
"People", "Print", "Vegetation",
"Website"; some of them may have sub-keywords.

Export the photos in JPEG format to a "Exported"
directory. Do not resize them and use ProPhotoRGB (if your
display doesn't have a large gamut, use sRGB) and quality
90...100. (IrfanView can show color-managed photos.)

Export some of the photos in JPEG format to a "Print"
directory. Do not resize them and use sRGB (printers have a much
smaller gamut than displays) and quality 100. Print the photos on
A4 paper.

Export some of the photos in JPEG format to a "Website"
directory. Resize them (within 900 * 900) and use sRGB (because
it's standard for the web) and quality 80.

Parameters

As a starting point, for outdoor daylight photos I use the
default editor settings with the following changes:

Tone curve: Linear.

Blacks: -40.

Shadows: 10.

Sharpness: 50.

Luminance noise reduction: 20.

Lens correction: by profile.

Vignette: -5.

Display calibration

It is crucialto calibrate the display on
which you'll see and edit your photos,
in the environmental light that you are going to use, at the
preferred display brightness.

Turn on your display with at least
30 minutes before you try to calibrate it.

The illumination from your room
(at display level, non-incident, with the display off) should be
30...60 lux. You should also have a color temperature of about
4'000...4'500 kelvin, but this looks cold in a home, so you need
to have a separate lighting fixture.

If possible, calibrate your
display with a calibrating device. Hardware calibration will not
make your display better, it just makes it display images
according to a colorimetric standard, in the limits of its
hardware capabilities. Set the calibration target to D65
(color temperature = 6'500 kelvin, gamma = 2.2).

Printing

Do the printing on a photo printer.

A home printer provides all the necessary image quality, when
the printing is performed at the maximum quality and with
consumables (= paper and ink) of the highest quality. You should
disable all forms of photo processing within the printer
software.

I prefer to use a folder with a ring binder as a photo album,
even though I have to perforate each photo by hand, because:

The photos are not covered by anything when you view
them.

Photos can be grouped in categories because photos made
later can be easily inserted anywhere in between.

It's faster than sticking photos to an album's pages, and
it doesn't waste the paper used for the album's pages.

The photos can be easily moved to a more appropriate
album (like a thicker one).

Printing the photos with a border minimizes the effect of the
perforations and of the fingers (used to hold the photos while
flipping them).

The advantages of my home printer are:

Better color match to my display.

Immediate results (I don't have to go out to print).

The disadvantages of my home printer are:

The ink is sticky and that's a real fingerprint magnet.
The photos have to be kept to dry in a covered place, so that
dust would not stick to the fresh ink.

The advantages of a photo-developing machine are:

Many paper sizes.

The paper can be glossy or matte.

About 3 times cheaper than my home printer (for the same
size).

Outputs photos 10 times faster than my printer.

The photos are safe to touch immediately.

The disadvantages of a photo-developing machine are:

Difficult to find one which outputs proper colors, and
sometimes the results are not reproducible.

Because of the price, I prefer to output my photos on a
photo-developing machine.